Circuits with a direct injection of fuel into internal combustion engines comprise a controlled valve which may be engaged directly on a common rail distributing pressurized fuel to injectors. The valve is normally in a closed state and can be switched into an open state to uncover a passage and allow fuel out, thus making it possible constantly to regulate the pressure in the injection circuit.
Known amongst others are valves comprising a tubular body in which an axially mobile central shaft shuts off or uncovers the fuel outlet passage. The central shaft has a planar end in contact with the plunger of the electromagnet and a pointed or hemispheric end which collaborates with a fixed conical seat at the center of which the outlet passage opens. In normal operation the passage remains closed, the plunger of the electromagnet exerting on the central shaft a closure force that is greater than the opposite force exerted on the pointed end of the shaft by the pressurized fuel flowing along the common rail.
The mobile shaft is axially guided in a central bore of the body. In order to shut off the outlet passage, the central bore and the mobile shaft each need to have an excellent surface finish and a very small degree of non-cylindricity. The assembly should also have a small degree of non-coaxiality. In addition, given the high and repeated loads it experiences, the mobile shaft needs to be made from a high quality steel, for example a 100 Cr6 steel with quench and temper in order to obtain a surface hardness of the order of 700 HV.
This high precision machining leads to technological complexity which it has become an urgent matter to simplify by proposing valves that operate perfectly while at the same time being simple to manufacture and to assemble.